build: add conditional BuildRequires libuv-devel in fedora.spec
build: add conditional BuildRequires libuv-devel in fedora.spec

Without this, RPM spec builds done in a chroot (e.g. Fedora, RHEL etc)
will not pull in libuv headers or libs, and hence pmseries and libpcp_web
will not be built.

This is now version conditional for Fedora and RHEL (and presumabely
Centos) builds. As far as I can work out, libuv-devel is not available
on SuSE (according to qa/admin/other-packages/unavailable). Not sure
about any other RPM based platforms - if anyone knows (Ken?), please
update as appropriate.

modified:   build/rpm/fedora.spec

adfernandes/pcp,adfernandes/pcp,adfernandes/pcp,adfernandes/pcp,adfernandes/pcp,adfernandes/pcp,adfernandes/pcp,adfernandes/pcp